Rear Axle

“A Rear axle is a shaft which is lie between the differential & driving wheels & transmit power from the differential to the driving wheels.” 

Its consists of two halves connected by the differential, one part is known as Half Shaft. Inner end of the half shaft is connected to the Sun gear of the differential & the outer end to the driving wheels.

Functions of Rear Axles

The rear axles perform the following two functions. 

1. Carry the weight of the vehicle. 

2. To rotate & transmit the power from engine to the wheels.

3. Provide the final speed reduction between drive shaft & axle shaft through final drive gears.

4. Act as a Thrust & torque reaction member during acceleration & breaking.

5. Changing drive shaft rotation by 90 degree to rotate the axle shaft.

Types of Rear Axles Housing

The rear axles differ from the front axle in that it contain no joint at its outer ends. Its housing are two types

1. Banjo type 

2. Split type 

1. Banjo Type – 

In this type the axle is single unit & final drive assembly is carried in a separate casing which is bolted to the axle housing. The banjo construction used for axle cases of smaller & lighter vehicles. 

2. Split type – 

In this arrangement the central housing contain the final drive & its fitted with a tube on each side to carry the half axles & bearings. 

Types of Axles

1. According to method of supporting the rear axles & mounting the rear wheels the rear axles are following three types

1.Half Floating rear axle. 

2. Three Quarter floating rear axle 

3. Fully floating rear axle

1.Half Floating rear axle- 

In this type of rear axle Bearings are inside the axle casing. The axle of the wheel is at the Centre of the axle casing. The wheel are fitted at the two ends of the axle by means of a Key, Bolt & Nut. The whole weight is transmitted to the suspension spring then to the axle case, rear axle, wheel & finally to the ground.

2.Three Quarter Floating rear axle- 

In this type of rear axle is fitted inside the axle casing. The Bearing are on the outer side between the wheel & the axle casing. The weight of the vehicle is supported partly by axle case & partly by the axle. The major advantages is the major part of the load is taken by the axle casing & not by the axle.

3. Fully Floating rear axle- 

In this type of rear axle Bearing are between the wheel & axle case. The axle is introduced inside the axle case. The entire weight of the vehicle is supported by axle case & wheels. This type of axle is very strong & is used for Heavy duty vehicles.

2. According to Power transmission

1. Live or Drive Axle- 

It's support the weight of vehicle & drive the wheels that connected to half shaft.

2. Dead or Drive-less Axle

It's support the weight of vehicle but not drive the wheels that connected to half shaft.

S.NO	Parameters	Semi-Floating	Three-Quarter Floating	Full Floating
1	Cost	Low	Medium	High
2	Sustaining of Vehicle load	Yes, Vertical load is taken by half shaft bearings.	Yes, Vertical load is taken by single bearing placed over the axle casing.	Nil
3	Existence of side load	The side load is present.	The side load is present.	Nil
4	Driving torque to the wheels	Yes	Yes	Yes
5	Placement of bearing	The Bearing is placed within the axle casing.	The Bearing are placed over the axle casing.	The bearing is placed within the axle casing.
6	Application	In medium capacity vehicles.	In low & medium capacity vehicles.	In heavy capacity vehicles.

Loads on Rear Axles

The different forces acting on the rear axles are-

1.  Share of load which may be one-half of the weight of vehicle when it's stationary. The rear axle is thought to be beam supported at the ends & loaded at two positions. he loads induces share force & bending moment in axle shaft.

2.  Driving thrust produced in the road wheels due to driving torque produced in the engine. this thrust needed to transmitted from axle casing to the chassis frame & body of the vehicle. This is achieved by using members called radius rods or thrust members, that connect the axle & chassis frame in longitudinal directions.

3. Bending moment due to offset of the weight of the vehicle applied through the spring seats & the wheels.

4. The end thrust due to side forces which develop because of wind & when the vehicle is cornering. The axle held in position against the side thrust by employing panhard rods.

5. Bending moment due to end thrust & it's reactions offered by wheels.

6. Force due to application of brakes. The vehicle tends to continuous in forward directions while axle comes to rest.

7. Turning or torque of the rear wheels & their consequents reactions.

Troubleshooting of Rear Axles: Fault, Probable Causes & Remedies

1. Back Lash

- Worm Splines of axle shaft : Replace the axle shaft

- Worm Universal Joints : Replace

- Worm Bearing of Differential : Replace

- Worm Thrust Washer of Differential Side Gears : Replace

- Axle Shaft Nut Loose : Tighten the Nut

2. Axle Noisy On Acceleration

- Loose Pinion Bearing : Make Proper Adjustment

- Rough Pinion Bearing : Replace

- Faulty Adjustment of Pinion & Ring Gears : Check & Readjust

3. Axle Noisy On Coast

- End Paly in Pinion Shaft : Check & Readjust

- Excessive Backlash in Pinion & Ring Gears : Check & Readjust

4. Axle Noisy On Both Acceleration & Coast

- Worm Pinion & Ring Gears or Differential Gears : Replace the Worm Gears

- Excessive Backlash in Pinion & Ring Gears : Check & Readjust

- Worm or Defective Bearings : Replace

Tight Setting of Pinion & Ring Gears : Adjust the Setting